Siu-Cheong Yan

Timosaponin A-III induces autophagy preceding mitochondria-mediated apoptosis in hela cancer cells

Timosaponin A-III (TAIII), a saponin isolated from the rhizome of Anemarrhena asphodeloides, exhibits potent cytotoxicity and has the potential to be developed as an anticancer agent. Here, we provide evidence that TAIII induces autophagy in HeLa cells followed by apoptotic cell death. TAIII-induced autophagy was morphologically characterized by the formation of membrane-bound autophagic vacuoles recognizable at the ultrastructural level. TAIII-treated cells expressing green fluorescent protein (GFP)-labeled microtubule-associated protein 1 light chain 3 (LC3) displayed punctate fluorescence indicative of LC3 recruitment to the autophagosome. This was associated with the conversion of LC3-I (the cytosolic form) into LC3-II (the lipidated form located on the autophagosome membrane). TAIII treatment also induced mitochondrial dysfunction involving overproduction of reactive oxygen species and reduction of mitochondrial membrane potential accompanied by induction of mitochondrial permeability transition. Prolonged exposure to TAIII resulted in cytochrome c release and caspase-3 activation, events that signified the onset of apoptotic cell death. TAIII-induced autophagy preceded apoptosis, as evidenced by early autophagic vacuole formation, GFP-LC3 translocation, and LC3-II increase in the absence of caspase-3 cleavage. Notably, TAIII-mediated apoptotic cell death was potentiated by treatment with autophagy inhibitor 3-methyladenine or small interfering RNA against the autophagic gene beclin 1. These findings suggest that TAIII-elicited autophagic response plays a protective role that impedes the eventual cell death. In terms of structure-activity relationship, the sugar chain in TAIII is indispensable to the drug action, as the sugar-lacking aglycone sarsasapogenin did not induce autophagy and exhibited weaker cytotoxicity.

A selective G-quadruplex-based luminescent switch-on probe for the detection of nanomolar silver(I) ions in aqueous solution.

A G-quadruplex-based luminescent platinum(II) switch-on probe has been developed for the selective detection of nanomolar Ag(+) ions in aqueous solution.

Identification of natural product Fonsecin B as a stabilizing ligand of c-myc G-quadruplex DNA by high-throughput virtual screening

Fonsecin B has been identified as stabilizing ligand of c-myc G-quadruplex DNA using high-throughput virtual screening of a natural product database, and inhibited Taq polymerase-mediated DNA extension in vitro through stabilization of the G-quadruplex secondary structure.

Benzothiazole-substituted benzofuroquinolinium dye: a selective switch-on fluorescent probe for G-quadruplex

A new switch-on fluorescent probe containing the natural product cryptolepine analogue benzofuroquinolinium moiety (binding scaffold) and a benzothiazole moiety (signalling unit) shows a remarkable fluorescence enhancement selective for the G-quadruplex nucleic acid structure. Binding studies revealed that the highly selective response of the fluorescent probe arises from end-stack binding to G-quadruplex.

Rational design of berberine-based FtsZ inhibitors with broad-spectrum antibacterial activity.

Inhibition of the functional activity of Filamenting temperature-sensitive mutant Z (FtsZ) protein, an essential and highly conserved bacterial cytokinesis protein, is a promising approach for the development of a new class of antibacterial agents. Berberine, a benzylisoquinoline alkaloid widely used in traditional Chinese and native American medicines for its antimicrobial properties, has been recently reported to inhibit FtsZ. Using a combination of in silico structure-based design and in vitro biological assays, 9-phenoxyalkyl berberine derivatives were identified as potent FtsZ inhibitors. Compared to the parent compound berberine, the derivatives showed a significant enhancement of antibacterial activity against clinically relevant bacteria, and an improved potency against the GTPase activity and polymerization of FtsZ. The most potent compound 2 strongly inhibited the proliferation of Gram-positive bacteria, including methicillin-resistant S. aureus and vancomycin-resistant E. faecium, with MIC values between 2 and 4 µg/mL, and was active against the Gram-negative E. coli and K. pneumoniae, with MIC values of 32 and 64 µg/mL respectively. The compound perturbed the formation of cytokinetic Z-ring in E. coli. Also, the compound interfered with in vitro polymerization of S. aureus FtsZ. Taken together, the chemical modification of berberine with 9-phenoxyalkyl substituent groups greatly improved the antibacterial activity via targeting FtsZ.

Cyclometalated platinum(II) complexes as topoisomerase IIα poisons.

A platinum(II)-based major groove binder [Pt(II)(C^N)(C≡NR)(2)](+) (HC^N = 2-phenylpyridine (phpy), R = 2-naphthyl) was identified as a potent human topoisomerase IIα poison. It stabilizes the covalent TopoIIα-DNA cleavage complex and induces cancer cell death with potency significantly higher than the widely clinically used TopoIIα poison Vp-16.

Discovery of a natural product-like c-myc G-quadruplex DNA groove-binder by molecular docking.

The natural product-like carbamide (1) has been identified as a stabilizer of the c-myc G-quadruplex through high-throughput virtual screening. NMR and molecular modeling experiments revealed a groove-binding mode for 1. The biological activity of 1 against the c-myc G-quadruplex was confirmed by its ability to inhibit Taq polymerase-mediated DNA extension and c-myc expression in vitro, demonstrating that 1 is able to control c-myc gene expression at the transcriptional level presumably through the stabilization of the c-myc promoter G-quadruplex. Furthermore, the interaction between carbamide analogues and the c-myc G-quadruplex was also investigated by in vitro experiments in order to generate a brief structure-activity relationship (SAR) for the observed potency of carbamide 1.

G-Quadruplex conformational change driven by pH variation with potential application as a nanoswitch.

BACKGROUND G-Quadruplex is a highly polymorphic structure, and its behavior in acidic condition has not been well studied. METHODS Circular dichroism (CD) spectra were used to study the conformational change of G-quadruplex. The thermal stabilities of the G-quadruplex were measured with CD melting. Interconversion kinetics profiles were investigated by using CD kinetics. The fluorescence of the inserted 2-Aminopurine (Ap) was monitored during pH change and acrylamide quenching, indicating the status of the loop. Proton NMR was adopted to help illustrate the change of the conformation. RESULTS G-Quadruplex of specific loop was found to be able to transform upon pH variation. The transformation was resulted from the loop rearrangement. After screening of a library of diverse G-quadruplex, a sequence exhibiting the best transformation property was found. A pH-driven nanoswitch with three gears was obtained based on this transition cycle. CONCLUSIONS Certain G-quadruplex was found to go through conformational change at low pH. Loop was the decisive factor controlling the interconversion upon pH variation. G-Quadruplex with TT central loop could be converted in a much milder condition than the one with TTA loop. It can be used to design pH-driven nanodevices such as a nanoswitch. GENERAL SIGNIFICANCE These results provide more insights into G-quadruplex polymorphism, and also contribute to the design of DNA-based nanomachines and logic gates.

Rapid reduction of pentavalent antimony by trypanothione: potential relevance to antimonial activation

The dithiol trypanothione can reduce an antiparasitic pentavalent antimony agent to trivalent rapidly; this reduction process is both pH and temperature dependent and trypanothione may therefore play an important role in the activation of the drug.

A Novel Tetradentate Ruthenium(II) Complex Containing Tris(2- pyridylmethyl)amine (tpa) as an Inhibitor of Beta-Amyloid Fibrillation

We report herein the synthesis and application of a novel tetradentate ruthenium(II) complex 1 containing a tris(2-pyridylmethyl)amine (tpa) ligand as an inhibitor of β-amyloid fibrillogenesis. [Ru(tpa)(bt)]ClO(4) 1 (bt =2-acetylbenzo[b]thiophene-3-olate) showed significant inhibition of Aβ(1-40) peptide aggregation in vitro, which was confirmed by a Thioflavin T assay and transmission electron microscopy imaging.